ABSTRACT: In this investigation micron-sized monodisperse magnetic composite polymer particles with amino and amide functional groups were prepared considering their applications in biotechnology. First, polystyrene/poly (acrylic acid-acrylam- ide-N-N-methylene-bis-acrylamide) [PS/P(AA-AAm-MBAAm)] composite polymer particles were prepared by seeded copolymerization. The carboxyl groups present on or near the particles surface were modified by amine-nucleophile, ethylene diamine (EDA), through pre-activation with dicyclohexyl carbodiimide as coupling agent. The aminated particles were then magnetically modified and named as aminated-Fe3O4 composite particles. Formation of such magnetic composite particles was confirmed by scanning electron micrographs, FTIR-spectra and magnetic susceptibility measurement. The produced composite particles were paramagnetic. To see the relative hydrophilic character of the particles surface the adsorption behavior of trypsin (TR) as biomolecule was studied on PS particles and aminated-Fe3O4 composite particles. The magnitude of adsorbed TR on PS particles was higher than that on aminated-Fe3O4 composite particles.